Wide-band amplifier circuit with improved gain flatness

ABSTRACT

There is provided a wide-band amplifier circuit with improved gain flatness. The wide-band amplifier circuit includes a first resonant load unit connected to an operating power terminal, providing a preset first load, and forming a preset first resonant point, a second resonant load unit connected to the operating power terminal, providing a preset second load, and forming a second resonant point set to a frequency different from the first resonant point; a first amplification unit receiving operating power via the first load of the first resonant load unit, having an amplification band characteristic determined according to the first resonant point of the first resonant load unit, and amplifying an input signal; and a second amplification unit receiving operating power via the second load, having an amplification band characteristic determined according to the second resonant point, and amplifying an input signal from the first amplification unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No.10-2009-0051081 filed on Jun. 9, 2009, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wide-band amplifier circuit withimproved gain flatness, which is applicable to a 3^(rd) GenerationPartnership Project Long-Term Evolution (3GPP LTE) system, and moreparticularly, to a wide-band amplifier circuit with improved gainflatness, which satisfies a requirement for a wide band in a band lessthan 1 GHz in an upload link frequency band while having high gainflatness.

2. Description of the Related Art

3GPP LTE communications systems, considered to be 4G technology, aretechniques that aim at supporting various services based on packet datatransfer. The 3GPP LTE communications systems support a downlink peakdata rate of 100 Mbps and an upload link data rate of 50 Mbps withreference to a maximum bandwidth of 20 MHz. 3GPP LTE communicationssystems ensure improved data rates, low latency, efficient use offrequency resources, mobility, techniques optimized for packet datatransfer, and high service quality.

Such 3GPP LTE systems are mobile communications systems suitablyevolving for IP networks, so that frequencies and high-speed multimediaservices can be used more efficiently than by existing systems. 3GPP LTEmobile communications terminals support a downlink data rate of 30 Mbpsand an upload link data rate of 15 Mbps at a mobile speed of 120 km/h in20 MHz bandwidth. The 3GGP LTE communications terminals providehigh-quality high-speed multimedia services and are thus capable ofproviding mobile image services unlike 3.5G high-speed downlink packetaccess (HSDPA).

As for bands of less than 1 GHz in the upload link frequency band of a3GPP LTE communications system, there are total six bands: Band 5 (824MHz to 849 MHz), Band 6 (830 MHz to 840 MHz), Band 8 (880 MHz to 915MHz), Band 12 (698 MHz to 716 MHz), Band 13 (777 MHz to 787 MHz) andBand 14 (788 MHz to 798 MHz). A bandwidth from 697 MHz to 915 MHz,including band spacing, that is, a bandwidth of 217 MHZ, is required.

One example of the related art is a low noise amplifier (LNA) used foran ultra wide band (UWB) using a band between 3 GHz and 10 GHz. The LNAamplifies a signal by using an inverter structure, and obtains awide-band characteristic by using one of two feedback paths. Acapacitive parallel feedback path realizes a low and medium frequencyrange, and an inductive series feedback path realizes a high frequencyrange, so that the amplifier satisfies the wide band of about 7 GHz.

This related art LNA, having the above feedback structure, achieves highlinearity, but has limitations in that it is difficult to implement highgain, and additional circuits and currents need to be added forfeedback.

Another example of the related art is an LNA used for 802.11a systems.This LAN has a frequency band from 5.1 GHz to 5.9 GHz, and employs a2-stage amplifier having a cascode structure. The gain flatnessdesirably reaches 0.06 dB in this band.

However, a relatively large number of inductors are used in order toobtain a flat gain. This expands the chip size, thereby increasing theunit cost of a chip.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a wide-band amplifiercircuit with improved gain flatness, which satisfies a requirement for awide band in a band less than 1 GHz in an upload link frequency band ina 3GPP LTE system while having high gain flatness.

According to an aspect of the present invention, there is provided awide-band amplifier circuit with improved gain flatness, including: afirst resonant load unit connected to an operating power terminal,providing a preset first load, and forming a preset first resonantpoint; a second resonant load unit connected to the operating powerterminal, providing a preset second load, and forming a second resonantpoint set to a frequency different from the first resonant point; afirst amplification unit receiving operating power via the first load ofthe first resonant load unit, having an amplification bandcharacteristic determined according to the first resonant point of thefirst resonant load unit, and amplifying an input signal; and a secondamplification unit receiving operating power via the second load of thesecond resonant load unit, having an amplification band characteristicdetermined according to the second resonant point of the second resonantload unit, and amplifying an input signal from the first amplificationunit.

The first resonant load unit may include: a first inductance part havingone end connected to the operating power terminal and having presetinductance; a first resistor connected between the other end of thefirst inductance part and the first amplification unit; and a firstcapacitor connected to the other end of the first inductance part andthe ground.

The second resonant load unit may include: a first inductor having oneend connected to the operating power terminal; a second resistorconnected in parallel to the first inductor; a second inductance parthaving one end connected to the other end of the first inductor, and theother end connected to the second amplification unit; and a secondcapacitor connected between the other end of the first inductor and anoutput terminal.

The first amplification unit may include: a first metal oxidesemiconductor (MOS) transistor including a drain connected to the firstresonant load unit, a gate connected to a first bias voltage terminalvia a third resistor and a third capacitor, and a source; and a secondMOS transistor having a drain connected to the source of the first MOStransistor, a gate connected to a second bias voltage terminal via afourth resistor and connected to an input terminal via a first couplingcapacitor, and a source connected to the ground via a third inductancepart.

The second amplification unit may include a third MOS transistor havinga drain connected to the other end of the second inductance part, a gateconnected to a third bias voltage terminal via a fifth resistor andconnected to the first amplification unit via a second couplingcapacitor, and a source connected to the ground via a fourth inductancepart.

The first inductance part, the second inductance part, the thirdinductance part and the fourth inductance part may each be configured asa bonding pad having preset inductance.

According to another aspect of the present invention, there is provideda wide-band amplifier circuit with improved gain flatness, including: afirst resonant load unit including a first inductance part configured asa bonding pad having one end connected to an operating power terminal,providing a preset first load, and forming a preset first resonantpoint; a second resonant load unit including a second inductance partconfigured as a bonding pad having one end connected to the operatingpower terminal, providing a preset second load, and forming a secondresonant point set to a different frequency from the first resonantpoint; a first amplification unit receiving operating power via thefirst load of the first resonant load unit, having an amplification bandcharacteristic determined according to the first resonant point of thefirst resonant load unit, and amplifying an input signal; and a secondamplification unit receiving operating power via the second load of thesecond resonant load unit, having an amplification band characteristicdetermined according to the second resonant point of the second resonantload unit, and amplifying an input signal from the first amplificationunit.

The first inductance part may have one end connected to the operatingpower terminal and have preset inductance, and the first resonant loadunit may further include: a first resistor connected between the otherend of the first inductance part and the first amplification unit; and afirst capacitor connected between the other end of the first inductancepart and the ground.

The second resonant load unit may further include: a first inductorhaving one end connected to the operating power terminal, and the otherend connected to the second inductance part; a second resistor connectedin parallel to the first inductor; and a second capacitor connectedbetween the other end of the first inductor and an output terminal. Thesecond inductance part is connected between the other end of the firstinductor and the second amplification unit.

The first amplification unit may include: a first metal oxidesemiconductor (MOS) transistor including a drain connected to the firstresonant load unit, a gate connected to a first bias voltage terminalvia a third resistor and a third capacitor, and a source; and a secondMOS transistor including a drain connected to the source of the firstMOS transistor, a gate connected to a second bias voltage terminal via afourth resistor and connected to an input terminal via a first couplingcapacitor, and a source connected to the ground via a third inductancepart.

The second amplification unit may include a third MOS transistor havinga drain connected to the other end of the second inductance part, a gateconnected to a third bias voltage terminal via a fifth resistor andconnected to the first amplification unit via a second couplingcapacitor, and a source connected to the ground via a fourth inductancepart.

The first inductance part, the second inductance part, the thirdinductance part and the fourth inductance part may each be configured asa bonding pad having preset inductance.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a block diagram showing a wide-band amplifier circuit withimproved gain flatness according to an exemplary embodiment of thepresent invention;

FIG. 2 is a view showing a wide-band amplifier circuit with improvedgain flatness in detail according to an exemplary embodiment of thepresent invention;

FIG. 3 is an equivalent circuit diagram of a bonding pad according to anexemplary embodiment of the present invention;

FIG. 4 is a graph showing the characteristic of amplification gain of anamplifier circuit according to an exemplary embodiment of the presentinvention; and

FIG. 5 is a graph showing the characteristic of output impedance of anamplifier circuit according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

The invention may, however, be embodied in many different forms andshould not be construed as being limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art. Like reference numerals in thedrawings denote like elements.

FIG. 1 is a block diagram of a wide-band amplifier circuit with improvedgain flatness, according to an exemplary embodiment of the presentinvention.

Referring to FIG. 1, a wide-band amplifier circuit with improved gainflatness, according to an exemplary embodiment of the present invention,includes: a first resonant load unit 100 connected to an operating powerterminal Vcc, providing a preset first load LD1, and forming a presetfirst resonant point RP1; a second resonant load unit 200 connected tothe operating power terminal Vcc, providing a preset second load LD2,and forming a second resonant point RP2 set to a different frequencyfrom the first resonant point RP1; a first amplification unit 300receiving operating power through the first load LD1 of the firstresonant load unit 100, having an amplification-band characteristicdetermined according to the first resonant point RP1 of the firstresonant load unit 100, and amplifying an input signal; and a secondamplification unit 400 receiving operating power through the second loadLD2 of the second resonant load unit 200, having an amplification-bandcharacteristic determined according to the second resonant point RP2 ofthe second resonant load unit 200, and amplifying an input signal fromthe first amplification unit 300.

The first load LD1 is provided for the output impedance matching of thefirst amplification unit 300, and the second load LD2 is provided forthe output impedance matching of the second amplification unit 400.

FIG. 2 illustrates a wide-band amplifier circuit having improved gainflatness in detail according to an exemplary embodiment of the presentinvention.

Referring to FIG. 2, the first resonant load unit 100 includes a firstinductance part BP1 having one end connected to the operating powerterminal Vcc and having preset inductance, a first resistor R11connected between the other end of the first inductance part BP1 and thefirst amplification unit 200, and a first capacitor C11 connectedbetween the other end of the first inductance part BP1 and the ground.

Here, the first resistor R11 forms the first load LD1, and the firstinductance part BP1 and the first capacitor C11 form the first resonantpoint RP1.

Referring to FIG. 2, the second resonant load unit 200 includes a firstinductor L21 having one end connected to the operating power terminalVcc, a second resistor R22 connected in parallel to the first inductorL21, a second inductance part BP2 having one end connected to the otherend of the first inductance part BP1 and the other end connected to thefirst amplification unit 200, and a second capacitor C22 connectedbetween the other end of the first inductor L21 and an output terminalOUT.

Here, the second inductance part BP2 forms the second load LD2. Theinductance of the parallel circuit of the second inductance part BP2 andthe first inductor L21, and the second capacitor C22 form the secondresonant point RP2.

Referring to FIG. 2, the first amplification unit 300 may be configuredas a single transistor, or into a cascode type that is advantageous interms of isolation.

The first amplification unit 300, when configured into a cascode type,includes a first metal oxide semiconductor (MOS) transistor M21 and asecond MOS transistor M22. The first MOS transistor M21 has a drainconnected to the first resonant load unit 100, a gate connected to afirst bias voltage terminal Vb1 via a third resistor R33 and a thirdcapacitor C33, and a source. The second MOS transistor M22 has a drainconnected to the source of the first MOS transistor M21, a gateconnected to a second bias voltage terminal Vb2 via a fourth resistorR34 and also connected to an input terminal IN via a first couplingcapacitor CC1, and a source connected to the ground via a thirdinductance part BP3.

Referring to FIG. 2, the second amplification unit 400 may be configuredas a single transistor, or into a cascode type that is advantageous interms of isolation.

The second amplification unit 400, when configured as a singletransistor, may include a third MOS transistor M43 having a drainconnected to the other end of the second inductance part BP2, a gateconnected to a third bias voltage terminal Vb3 via a fifth resistor R45and also connected to the first amplifier 300 via a second couplingcapacitor CC2, and a source connected to the ground via a fourthinductance part BP4.

Referring to FIGS. 1 and 2, in the wide-band amplifier circuit accordingto the embodiment of the present invention, the first inductance partBP1, the second inductance part BP2, the third inductance part BP3 andthe fourth inductance part BP4 may each be configured as a bonding padhaving preset inductance.

In this case, a separate inductor device for providing inductance isunnecessary, thereby contributing to a reduction in size.

FIG. 3 is an equivalent circuit diagram of a bonding pad according to anexemplary embodiment of the present invention.

Referring to FIG. 3, the bonding pad, according to an exemplaryembodiment of the present invention, may be equivalently expressed as acircuit in which inductors L1 and L2 and resistors R1 and R2 areconnected in series, a single capacitor C1 is connected between one endof this serial circuit and the ground, and another capacitor C2 isconnected between the other end of the serial circuit and the ground.

That is, the resistors R1 and R2 and the capacitors C1 and C2 areparasitic components, having a negligibly small value in a band lowerthan 1 GHz. Therefore, the bonding pad may be equalized only with theinductance of the inductors L1 and L2.

FIG. 4 is a graph showing the characteristics of amplification gain ofan amplifier circuit according to an exemplary embodiment of the presentinvention.

In FIG. 4, ‘S21_First’ is a curve representing the characteristic of theamplification gain of the first amplification unit 300, ‘S21_Second’ isa curve representing the characteristic of the amplification gain of thesecond amplification unit 400, and ‘S21_Total’ is a curve representingthe characteristic of the total amplification gain of the firstamplification unit 300 and the second amplification unit 400.

FIG. 5 is a graph showing the characteristic of output impedance of anamplifier circuit according to an exemplary embodiment of the presentinvention.

In FIG. 5, ‘S22_First’ is a curve representing the characteristic ofoutput impedance of the first amplification unit 300, ‘S22_Second’ is acurve representing the characteristic of output impedance of the secondamplification unit 400, and ‘S22_Total’ is a curve representing thecharacteristic of total output impedance of the first amplification unit300 and the second amplification unit 400.

The operation and effect of the invention will now be described indetail with reference to accompanying drawings.

Referring to FIGS. 1 through 5, the wide-band amplifier circuit withimproved gain flatness will now be described. As shown in FIG. 1, thewide-band amplifier includes the first resonant load unit 100, thesecond resonant load unit 200, the first amplification unit 300, and thesecond amplification unit 400.

The first resonant load unit 100 is connected to an operating powerterminal Vcc, provides a preset first load LD1 for output impedancematching and forms a first resonant point RP1 preset for a wideamplification band.

The second resonant load unit 200 is connected to the operating powerterminal Vcc, provides a second load LD2 preset for output impedancematching, and forms a second resonant point RP2 set to a differentfrequency from the first resonant point RP1 for the wide amplificationband.

For example, if an amplification band is set, the first resonant pointRP1 may be set to the start point of the amplification band, and thesecond resonant point RP2 may be set to the end point of theamplification band. Assuming that the bandwidth is about 215 MHz, thefrequency at the start point is 700 MHz and the frequency at the endpoint is 915 MHz, the first resonant point RP1 may be set to 700 MHz,which the start point of the amplification band, and the second resonantpoint RP2 may be set to 915 MHz, which is the end point of theamplification band. In contrast, the second resonant point RP2 may beset to 700 MHz, which is the start point of the amplification band, andthe first resonant point RP1 may be set to 915 MHz, which is the endpoint of the amplification band.

The first amplification unit 300 receives operating power through thefirst load LD1 of the first resonant load unit 100. Also, the firstamplification unit 300 has an amplification-band characteristicdetermined according to the first resonant point RP1 of the firstresonant load unit 100, amplifies an input signal supplied through theinput terminal IN, and outputs it to the second amplification unit 400.

Subsequently, the second amplification unit 400 receives operating powerthrough the second load LD2 of the second resonant load unit 200. Also,the second amplification unit 400 has an amplification-bandcharacteristic determined according to the second resonant point RP2 ofthe second resonant load unit 300, amplifies an input signal from thefirst amplification unit 200, and outputs it to the output terminal OUT.

Referring to FIGS. 1 and 2, the first resonant load unit 100 includesthe first inductance part BP1, the first resistor R11 and the firstcapacitor C11.

The first resonant load unit 100 provides the first load LD1 determinedby the first inductance part BP1, the first resistor R11 and the firstcapacitor C11 to thereby achieve the output impedance matching of thefirst amplification unit 300. Also, the first resonant load unit 100forms the first resonant point RP1 determined by the first inductancepart BP1 and the first capacitor C11 to thereby determine theamplification band of the first amplification unit 300.

In addition, referring to FIG. 2, the second resonant load unit 200includes the first inductor L21, the second resistor R22, the secondinductance part BP2 and the second capacitor C22.

The second resonant load unit 200 provides the second load LD2determined by the first inductor L21, the second resistor R22, thesecond inductance part BP2 and the second capacitor C22 to therebyachieve the output impedance matching of the second amplification unit400. Also, the second resonant load unit 200 forms the second resonantpoint RP2 determined by the first inductor L21, the second inductancepart BP2 and the second capacitor C22 to thereby determine theamplification band of the second amplification unit 400.

The amplification bands of the first amplification unit 300 and thesecond resonant load unit 200 are determined by the first resonant loadunit 100 and the second resonant load unit 200. The amplification bandof the amplifier circuit of the present invention can be widened bysetting the first resonant point RP1 of the first resonant load unit 100and the second resonant point RP2 of the second resonant load unit 200to different frequencies.

In particular, in the amplifier circuit of the embodiment of the presentinvention, the first inductance part BP1 of the first resonant load unit100 and the second inductance part BP2 of the second resonant load unit200 may be configured as bonding pads. This is advantageous in terms ofa size reduction because a separate inductance device may not be used.

Referring to FIG. 2, the first amplification unit 300 may be configuredas a single transistor, or into a cascode type that is advantageous interms of isolation.

For example, the first amplification unit 300, when configured into acascode type, may include the first MOS transistor M21 and the secondMOS transistor M22 as shown in FIG. 2.

The first MOS transistor M21 of the first amplification unit 300 isoperated by a first bias voltage Vb1 supplied via the third resistor R33and the third capacitor C33. The second MOS transistor M22 of the firstamplification unit 300 is operated by a second bias voltage Vb2 suppliedvia the fourth resistor R33.

Accordingly, the input signal input via the input terminal IN isamplified by the first MOS transistor M21 and the second MOS transistorM22.

Referring to FIG. 2, the second amplification unit 400 may be configuredas a single transistor, or into a cascode type that is advantageous interms of isolation.

For example, when the second amplification unit 400 is configured as asingle transistor, the second amplification unit 400 may include a thirdMOS transistor M43.

The third MOS transistor M43 is operated by a third bias voltage Vb3supplied via a fifth resistor R45.

Accordingly, a signal from the first amplification unit 300 is amplifiedby the third MOS transistor M43.

As described above, referring to FIGS. 1 and 2, in the wide-bandamplifier of the embodiment of the present invention, the firstinductance part BP1, the second inductance part BP2, the thirdinductance part BP3 and the fourth inductance part BP4 may each beformed as a bonding pad with preset inductance.

In this case, a separate inductor device for providing inductance isunnecessary, which contributes to a reduction in size.

Referring to FIG. 3, the bonding pad, according to the embodiment of thepresent invention, may be equivalently expressed as a circuit in whichinductors L1 and L2 and resistors R1 and R2 are connected in series, asingle capacitor C1 is connected between one end of this serial circuitand the ground, and another capacitor C2 is connected between the otherend of the serial circuit and the ground.

Here, the resistors R1 and R2 and the capacitors C1 and C2 are parasiticcomponents, and thus have relatively small values. The inductors L1 andL2 have relatively larger values than the values by the parasiticcomponents.

Hereinafter, a description is made based on a two-port circuit networktheory, referring to FIGS. 1 through 5.

The amplifier circuit of an exemplary embodiment of the presentinvention, based on the cascade-connected two-port circuit networktheory, may realize a flat gain and a wide-band frequency responsewithin a desired band since the gain characteristic and output impedancematching of the first amplifier circuit 300 overlap the characteristicof the second amplification unit 400.

That is, according to the two-port circuit network theory, theamplification gain S21total of two cascade-connected circuit networks,that is, the first and second amplification units 300 and 400 isexpressed as Equation 1 below:S21total=K(S21first)*(S21second), where K=1/(1−S22first*S11second)  Eq.1

The output impedance matching S22total of the first and secondamplification units 300 and 400, the two cascade-connected circuitnetworks, is expressed as Equation 2 below:S22total=(S22second)+K(S12second)*(S21second)*(S22first),where K=1/(1−S22first*S11second)  Eq. 2

When the output impedance of the first amplification unit 300, which isthe first circuit network, and the input impedance of the secondamplification unit 400, which is the second circuit network are matchedat −10 dB or lower, S22first*S11second is considered to be almost zero.Therefore, K ideally becomes a constant 1.

The total gain of the first and second amplification units 300 and 400,the two cascade-connected circuit networks, is equal to the sum of therespective gains of the circuit networks. When the output impedance ofeach stage is matched at −10 dB or lower, K, S12 second and S21secondbecome one. Therefore, the output impedance matching of the firstamplification unit 300, which is the first circuit network overlaps theoutput impedance matching of the second amplification unit 400, which isthe second circuit network, thereby determining a total output impedancematching curve.

Referring to FIG. 2, the amplifier circuit of the embodiment of thepresent invention has high gain and linearity so as to be used at thelast stage of the upload link. This high gain may be achieved due to thetwo-stage amplifier configuration.

First, the first amplification unit 300 has a cascode structure usingthe first resonant load unit 100 including the first resistor R11. Thisstructure realizes a gain characteristic having a wide-band frequencyresponse but causes undesirable low linearity. Therefore, the resistancevalue of the first resonant load unit 100 is selected so as to satisfythe linearity required by the first amplification unit 300. Also, thecascode structure of the first amplification unit 300 ensures theinput/output isolation. For the output impedance matching, the firstresonant load unit 100 of the first amplification unit 300 employs theinductor of the bonding pad BP1 connected to supply operating voltageVcc from the outside, and the first capacitor C11 serving to supply anideal operating voltage by causing AC components to flow to the ground.That is, the output impedance matching of the first amplification unit300 is induced by using the inductance and capacitance that arenecessarily used, without adding a new device.

The second amplification unit 400 has a common source structure using anopen drain. The second resonant load unit 200 of the secondamplification unit 400 includes the second inductance part BP2 that maybe formed as a bonding pad.

The second amplification unit 400 has an amplification frequency bandrange less than 1 GHz. In this case, if an inductor is realized as achip, the size increases undesirably, raising the chip price. To preventthis price increase from occurring, the open drain structure in whichthe inductor is provided outside is selected, allowing for economicalchip implementation.

Furthermore, the second inductance part BP2 is used for the second loadLD2 in the second resonant load unit 200, thereby enhancing linearity.The output impedance of the second amplification unit 400 is induced byinductance caused by the parallel connection between the first inductorL21 and the second inductance part BP2, and the second capacitor C22.

In FIG. 4, ‘S21_First’ is a curve representing the characteristic of theamplification gain of the first amplification unit 300, ‘S21_Second’ isa curve representing the characteristic of the amplification gain of thesecond amplification unit 400, and ‘S21_Total’ is a curve representingthe characteristic of the total amplification gain of both the firstamplification unit 300 and the second amplification unit 400.

Referring to ‘S21_Total’ of FIG. 4, it can be seen that theamplification band of the amplifier circuit is about 215 MHz from about700 MHz to about 915 MHz.

In FIG. 5, ‘S22_First’ is a curve representing the characteristic of theoutput impedance of the first amplification unit 300, ‘S22_Second’ is acurve representing the characteristic of the output impedance of thesecond amplification unit 400, and ‘S22_Total’ is a curve representingthe characteristic of the total output impedance of the firstamplification unit 300 and the second amplification unit 400.

Referring to the graph ‘S22_Total’ of FIG. 5, it can be seen that theoutput impedance of the amplifier circuit, according to the presentinvention, is about −10 [dB] in the range of about 700 MHz to about 915MHz.

FIGS. 4 and 5 are confirmed by the result of a simulation of the abovetheoretical contents of the present invention. FIG. 4 shows the gain ofthe amplifier circuit according to the present invention. As describedabove in the cascade-connected two-port circuit network theory, it canbe seen that the total gain and bandwidth of the entire amplifiercircuit is determined by combining ‘S21_First’ representing the gain ofthe first amplification unit, which is the first circuit network, with‘S21_Second’ representing the gain of the second amplification unit,which is the second circuit network. In FIG. 4, the total gain of theamplifier circuit is represented by ‘S21_Total’.

It can be confirmed from FIG. 4 that desired flatness may be obtainedwithin a desired band by controlling the resonant frequency and gainflatness of each circuit network. Here, a flat gain curve of 0.04 dB maybe obtained between 700 MHz and 915 MHz, which is a frequency bandrequired by the amplifier circuit of the present invention.

FIG. 5 shows the output impedance matching of the amplifier circuit ofthe present invention. As described above, FIG. 5 illustrates‘S22_First’ having the resonant point of the first amplification unit300, which is the first circuit network, by using the first inductancepart BP1 and the first capacitor C11. FIG. 5 also illustrates‘S22_Second’ having the resonant point of the second amplification unit400, which is the second circuit network, by the inductance caused bythe first inductor L21 and the second inductance part BP2, and thesecond capacitor C22.

Accordingly, it can be seen that as the resonance frequencies overlapeach other, ‘S22_Total’, a curve representing the final output impedancematching can be obtained.

As described so far, according to the present invention, gain flatnessamong the specifications of an RF amplifier in a transmitter systemdetermines a band usable by a system. Moreover, providing flat gainwithin a required band may ensure high transmitter performance in areassuch as stable linearity and error vector magnitude (EVM). For in-bandgain characteristics and output impedance matching, most of wide-bandamplifiers employ an inductor (L) and a capacitor (C) at an outputterminal, or a feedback structure. However, if the inductor (L) and thecapacitor (C) are used to realize a wide-band amplifier, thisundesirably increases the number of components being used. If thefeedback structure is used, high gain cannot be obtained. Therefore, theamplifier circuit of the present invention may be considered to be astructure suited for high gain and flatness without increasing thenumber of components being used.

As set forth above, according to exemplary embodiments of the invention,in a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE)system, a wide band required in a band less than 1 GHz in an upload linkfrequency band is satisfied, and high gain flatness is achieved.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A wide-band amplifier circuit with improved gain flatness,comprising: a first resonant load unit connected to an operating powerterminal, configured to provide a preset first load and form a presetfirst resonant point; a second resonant load unit connected to theoperating power terminal, configured to provide a preset second load andform a second resonant point set to a frequency different from that ofthe first resonant point; a first amplification unit configured toreceive operating power via the first load of the first resonant loadunit, have a first amplification band characteristic determinedaccording to the first resonant point of the first resonant load unit,and amplify an input signal; and a second amplification unit configuredto receive operating power via the second load of the second resonantload unit, have a second amplification band characteristic determinedaccording to the second resonant point of the second resonant load unit,and further amplify the amplified input signal outputted from the firstamplification unit, wherein the first resonant load unit comprises: afirst inductance part having one end connected to the operating powerterminal and having a first preset inductance; a first resistorconnected between the other end of the first inductance part and thefirst amplification unit; and a first capacitor connected between theother end of the first inductance part and the ground.
 2. The wide-bandamplifier circuit of claim 1, wherein the second resonant load unitcomprises: a first inductor having one end connected to the operatingpower terminal; a second resistor connected in parallel to the firstinductor; a second inductance part having one end connected to the otherend of the first inductor, and the other end connected to the secondamplification unit; and a second capacitor connected between the otherend of the first inductor and an output terminal.
 3. The wide-bandamplifier circuit of claim 2, wherein the first amplification unitcomprises: a first metal oxide semiconductor (MOS) transistor includinga drain connected to the first resonant load unit, a gate connected to afirst bias voltage terminal via a third resistor and also connected to athird capacitor, and a source; and a second MOS transistor having adrain connected to the source of the first MOS transistor, a gateconnected to a second bias voltage terminal via a fourth resistor andconnected to an input terminal, which is configured to receive the inputsignal, via a first coupling capacitor, and a source connected to theground via a third inductance part.
 4. The wide-band amplifier circuitof claim 3, wherein the second amplification unit comprises a third MOStransistor having a drain connected to the other end of the secondinductance part, a gate connected to a third bias voltage terminal via afifth resistor and connected to the first amplification unit via asecond coupling capacitor, and a source connected to the ground via afourth inductance part.
 5. The wide-band amplifier circuit of claim 4,wherein the first inductance part, the second inductance part, the thirdinductance part and the fourth inductance part are each configured as abonding pad, the second, third, and fourth inductance parts having asecond, a third, and a fourth preset inductances, respectively.
 6. Awide-band amplifier circuit with improved gain flatness, comprising: afirst resonant load unit comprising a first inductance part configuredas a bonding pad having one end connected to an operating powerterminal, the first resonant load unit being configured to provide apreset first load and form a preset first resonant point; a secondresonant load unit comprising a second inductance part configured as abonding pad having one end connected to the operating power terminal,the second resonant load unit being configured to provide a presetsecond load and form a second resonant point set to a frequencydifferent from that of the first resonant point; a first amplificationunit configured to receive operating power via the first load of thefirst resonant load unit, have a first amplification band characteristicdetermined according to the first resonant point of the first resonantload unit, and amplify an input signal; and a second amplification unitconfigured to receive operating power via the second load of the secondresonant load unit, have a second amplification band characteristicdetermined according to the second resonant point of the second resonantload unit, and further amplify the amplified input signal outputted fromthe first amplification unit, wherein the first inductance part has oneend connected to the operating power terminal and has a first presetinductance, and the first resonant load unit further comprises: a firstresistor connected between the other end of the first inductance partand the first amplification unit; and a first capacitor connectedbetween the other end of the first inductance part and the ground. 7.The wide-band amplifier circuit of claim 6, wherein the second resonantload unit further comprises: a first inductor having one end connectedto the operating power terminal, and the other end connected to thesecond inductance part; a second resistor connected in parallel to thefirst inductor; and a second capacitor connected between the other endof the first inductor and an output terminal, wherein the secondinductance part is connected between the other end of the first inductorand the second amplification unit.
 8. The wide-band amplifier circuit ofclaim 7, wherein the first amplification unit comprises: a first metaloxide semiconductor (MOS) transistor including a drain connected to thefirst resonant load unit, a gate connected to a first bias voltageterminal via a third resistor and also connected to a third capacitor,and a source; and a second MOS transistor including a drain connected tothe source of the first MOS transistor, a gate connected to a secondbias voltage terminal via a fourth resistor and connected to an inputterminal, which is configured to receive the input signal, via a firstcoupling capacitor, and a source connected to the ground via a thirdinductance part.
 9. The wide-band amplifier circuit of claim 8, whereinthe second amplification unit comprises a third MOS transistor having adrain connected to the other end of the second inductance part, a gateconnected to a third bias voltage terminal via a fifth resistor andconnected to the first amplification unit via a second couplingcapacitor, and a source connected to the ground via a fourth inductancepart.
 10. The wide-band amplifier circuit of claim 9, wherein the thirdinductance part and the fourth inductance part are each configured as abonding pad, the second, third and fourth inductance parts having asecond, a third and a fourth preset inductances, respectively.